He was born in Glasgow and emigrated to Australia at the age of 12. He now lives in Los Angeles. Prior to his career as a presenter, he was a student at Bradfield College (Sydney) then became an advertising executive.

McMullen's career as a host and presenter began as a presenter with Arena Television's Exclusive news on Foxtel and with appearances in major advertising campaigns for Westfield and Gloria Jean's. Darren appears weekly on MTV Australia's The Lair, his own live music show where he interviews bands and entertains the party goers.

In addition to hosting on The Lair, McMullen also hosted a monthly car DVD called Ignition.

In 2009, he hosted Commercial Breakdown on Channel Nine. In 2010, McMullen signed with Channel Seven as host of their new primetime game show Minute to Win It.

On 29 June 2011, McMullen debuted as the host of the prime time reality show Love in the Wild on NBC in the USA and CTV in Canada. McMullen also hosts the UK version of Minute to Win It on ITV2 and hosted Series 2 of The Magicians on BBC One.